docs: def memorized_ttinfo(*args):
      '''Create only one instance of each distinct tuple'''
      try:
          return _ttinfo_cache[args]
      except KeyError:
          ttinfo = (
                  memorized_timedelta(args[0]),
                  memorized_timedelta(args[1]),
                  args[2]
                  )
          _ttinfo_cache[args] = ttinfo
          return ttinfo